This invention relates to a solid state imaging device and, more particularly, to a solid state imaging device in which the charge integrating time and the blooming resistance for each pixel are constant regardless of pixel positions in a light receiving area.
Recently, a solid state imaging device using light receiving elements of amplification type as pixels has been proposed. As a light receiving element of amplification type, there is known a so-called Charge Modulation Device (hereinafter abbreviated as a CMD), for example. This CMD type light receiving element is described in detail, by way of example, in a paper entitled "A NEW MOS IMAGE SENSOR OPERATING IN A NON-DESTRUCTIVE READOUT MODE", pp. 353-356, Proceedings of International Electron Device Meeting (IEDM), 1986.
One example of arrangement of such a solid state imaging device using CMD type light receiving elements as pixels is shown in FIG. 1. CMDs 51-11, 51-12, . . . , 51-mn constituting respective pixels are arranged in the form of a matrix, and video voltage V.sub.DD (&gt;0) is commonly applied to respective drains of the CMDs. Respective gate terminals of a group of CMDs in each row arrayed in the X-direction are commonly connected to corresponding one of row lines 52-1, 52-2, . . . , 52-m, whereas respective source terminals of a group of CMDs in each column arrayed in the Y-direction are commonly connected to corresponding one of column lines 53-1, 53-2, . . . , 53-n. The column lines 53-1, 53-2, . . . , 53-n are commonly connected to a video line 56 through column select transistors 54-1, 54-2, . . . , 54-n, respectively, and also commonly connected to a line 57, in turn grounded to GND, through non-select transistors 55-1, 55-2, . . . , 55-n, respectively. The video line 56 is connected to a current-voltage conversion type preamplifier 58 with its input terminal virtually grounded, so that a video signal of negative polarity is time-serially read out at an output terminal 59 of the preamplifier 58.
Meanwhile, the row lines 52-1, 52-2, . . . , 52-m are connected to a vertical scanning circuit 60 and applied with signals .phi..sub.G1, .phi..sub.G2, . . . , .phi..sub.Gm, respectively. Gate terminals of the column select transistors 54-1, 54-2, . . . , 54-n are directly connected to a horizontal scanning circuit 61 and applied with signals .phi..sub.S1, .phi..sub.S2, . . . , .phi..sub.Sn, respectively. Gate terminals of the non-select transistors 55-1, 55-2, . . . , 55-n are connected to the horizontal scanning circuit 61 through inverters and applied with inverted ones of the signals .phi..sub.S1, .phi..sub.S2, . . . , .phi..sub.Sn, respectively. The CMDs are formed on the same single substrate which is applied with voltage V.sub.SUB (&lt;0).
FIG. 2 is a chart of signal waveforms for explaining operation of the solid state imaging device arranged as shown in FIG. 1. The signals .phi..sub.G1, .phi..sub.G2, . . . , .phi..sub.Gm applied to the row lines 52-1, 52-2, . . . , 52-m each comprise readout gate voltage V.sub.RD, reset voltage V.sub.RS, overflow voltage V.sub.OF and integrating voltage V.sub.INT. Then, each non-selected row is applied with the overflow voltage V.sub.OF during a horizontal blanking period t.sub.BL of the video signal and with the integrating voltage V.sub.INT during a horizontal video effective period t.sub.H thereof, whereas each selected row is applied with the readout gate voltage V.sub.RD during the horizontal video effective period t.sub.H and the reset voltage V.sub.RS during the horizontal blanking period t.sub.BL.
The signals .phi..sub.S1, .phi..sub.S2, . . . , .phi..sub.Sn applied to the gate terminals of the column select transistors 54-1, 54-2, . . . , 54-n are signals for respectively selecting the column lines 53-1, 53-2, . . . , 53-n, of which voltage values are set in such a manner as to turn off the column select transistors 54-1, 54-2, . . . , 54-n and on the non-select transistors 55-1, 55-2, . . . , 55-n at a low level and turn on the column select transistors and off the non-select transistors at a high level.
The conventional solid state imaging device thus arranged has, however, suffered from the following problems. First, while all the pixels in the same row are simultaneously reset, the signals are read out by sequential scanning. This results in different periods of integrating time between the pixel located on the left side of the light receiving surface and the pixel located on the right side thereof. Such a difference in the integrating time causes a serious obstruction in point of providing a high-speed shutter function to the solid state imaging device.
Secondly, while the overflow operation for the purpose of improving the blooming resistance is performed at once during the horizontal blanking period, the signals are read out by sequential scanning as mentioned above. Depending upon the pixel positions on the light receiving surface, therefore, amounts of exposure made after the end of the overflow operation until the readout of signals from the pixels are different from one another. This results in different degrees of the blooming resistance depending upon the horizontal positions of the pixels.
Thirdly, in the conventional solid state imaging device arranged as mentioned above, fixed pattern noise (FPN) occurs due to fluctuations in offset currents from pixel to pixel. As means for solving this problem, there has been proposed a method whereby a component of the fixed pattern noise is stored beforehand in a storage unit externally of the solid state imaging device, and this stored noise component is subtracted from the video signal obtained through accumulation of light. But, this method has a problem of complicating the system configuration. As means for overcoming the disadvantage of the above subtraction method using the external storage unit, there is known a photoelectric conversion device as disclosed in Japanese Patent Laid-Open No. 63-86471. However, the disclosed photoelectric conversion device has another problem that it is applicable only to the case of processing a signal from each pixel as a voltage value, but not to the case of reading out the pixel signal as a current value.